Afghan militants holding three United Nations workers hostage have extended a deadline for their threatened execution.

A man claiming to be a spokesman for the militants said today's (Wednesday's) deadline was extended to allow negotiations to continue. The man did not give a new deadline, and did not identify whom the militants were talking to.

A U.S. military spokesman said he could not discuss efforts to release the three hostages for security reasons.

The militants have threatened to execute the hostages unless authorities release all Taleban prisoners in U.S. custody, and unless all U.N. operations and foreign troops leave Afghanistan.

The captives are from Northern Ireland, the Philippines and the Serbian province of Kosovo. They were kidnapped in Kabul last week.